The present background of the invention concerns a device for postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation.
It is often necessary during brain surgery to remove a plug of bone from the cranium to provide the surgeon with access to the field of operation. The plug is sawed out and must be replaced in the cranium after the operation and fixed thereto. Such plugs have long been fixed back into the rest of the cranium by suturing with loops of steel wire that extend through both and then twisting together the projecting ends of the emplaced loops. The contact between the plug and the rest of the cranium is relatively unstable, however. The two halves do not fuse together very well. The scalp can also become inflamed. Another drawback to such an approach is that the wire considerably distorts the images obtained in postoperative computerized tomography and accordingly impedes definitive interpretation of the soft structures of the brain. Although using nonresorbable and physiologically compatible thread instead of wire does eliminate the last-mentioned drawback, the fixation of the plug to the rest of the skull is still unstable. The two parts can also be fixed with thin plates of compatible metal, titanium for instance (EP A 0 510 390). Such plates bridge the abutment between the parts and are screwed to both, also closing off bores introduced into the cranium prior to section. This approach, however, is also not very satisfactory. It is both complicated and time-consuming and hence not inexpensive.
With the aforesaid state of the art as a point of departure, the object of the present invention is a simpler and more rapid device for accurate and permanent postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation.
This object is attained in accordance with the present invention in a device of the aforesaid genus comprising a pin and two concavoconvex disks of a physiologically compatible metal or metal compound. The pin has a flat head at one end and one of the disks comes to rest against the head. Each disk has row of teeth extending along the edge of the concave side and a bore through the center. The shaft of the pin fits into the bore. The disks can be mounted on the shaft with the teeth on each one facing the teeth on the other. The second disk can be fastened to the shaft.
The inner disks in the aforesaid fixation device in accordance with the present invention are secured to the pins in the vicinity of the head The disks are then inserted through a slightly larger recess in the circumference of the plug, below the parts of the joint, with the shaft of the pin projecting out of the kerf between the plug and the rest of the cranium. The outer disk is then mounted over the section of pin projecting out of the kerf. The two disks are then approached until their teeth bite into the edges of both the plug and of the rest of the cranium. The second disk is then secured to the shaft.
Titanium is particularly appropriate for the physiologically compatible metal. Such titanium alloys as Ti6A6Va are also appropriate. A device made of titanium is of advantage because it will not distort postoperative computerized-tomography images. The inner disk can be mounted more stable on the shaft of the pin if the transition between the head of the pin and the shaft is conical and dimensioned to ensure that a disk resting against the head will be forced tight around the shaft. Slits can also extend radially outward from the bore through the first disk to be mounted on the shaft. The center of the disk can be depressed. Areas can be removed from the disks at regular intervals between the bore and the edge to conserve material. The device can be applied to the two halves of bone by a procedure similar in principle to blind riveting. Notches can accordingly be introduced into each shaft to prevent the second disk mounted thereon from sliding away from the head of the pin. If the second disk on the shaft is deformed in a direction opposite that of its concavoconvexity, the deformation alone will secure it to the shaft by compression. The shaft can also be threaded and accommodate a nut. The nut can be tightened against the second disk. The second disk will in every case be displaced until its teeth engage the two halves of the joint, creating the desired fixation of the plug back into the rest of the cranium at the adjacent edges.
The novel device can be easily and rapidly manipulated and accomplishes the desired accurate and permanent postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation.